In future, new requirements will be placed on fossil-fuel power plants, such as, for example, minimum emissions and additional CO2 separation. Currently, the most advanced power plant concept for CO2 separation is the Integrated Gasification Combined Cycle (IGCC). This technology encompasses gasification of the fuel before the actual combined cycle power plant (CCGT). Since CO2 capture measures always entail a loss of efficiency (8%-12%, depending on the basic technical requirements), when implementing an IGCC plant it is important to attempt to achieve a high degree of efficiency for the individual subprocesses.
One possible process, which can be connected upstream of a CCGT power plant, is the Siemens Fuel Gasification process protected under the trademark ‘SFG’. This autothermal entrained flow gasification process is suitable for using high-ash solid, liquid and gaseous feedstock. The feedstock is converted in a flame reaction, at temperatures (1500° C.-1800° C.) above the ash fusion temperature, into CO and H2 (main synthesis gas components). The hot raw gas and the molten slag are discharged from the reactor into a quench section located directly beneath the reactor in which both the raw gas and the slag are cooled to about 200° C.-250° C. by means of full quenching. The granulated slag formed by the rapid cooling is collected in the quench section and sluiced out. The cooled gas is guided laterally out of the quench section and sent to the cleaning stages.
With a process concept with full quench, the high temperature level of the hot gasification gas cannot be used for the generation of steam.
The use of the sensible heat for steam generation is, for example, conceivable in an IGCC application with combined heat and power generation and, in this context, would represent a possibility for increasing efficiency.
In the case of a gasification process with partial quench, thermal energy can be rendered usable in a downstream heat recovery steam generator; however, partial quench is associated with a lower steam content of the raw gas than is the case with full quench.